The present invention relates to methods and systems designed to detect vibrations in the drive train of a vehicle. More specifically, the invention relates to detection of drive train vibrations in a vehicle based on an evaluation of the rotational behavior of the wheels of the vehicle.
All mechanical systems (such as bridges, frames, machines, etc.) exhibit a natural frequency. The natural frequency of a body is the frequency at which that body will vibrate due to its own physical characteristics (mass, shape, boundary conditions, etc.) when the body is distorted and released. The drive train of a vehicle is a mechanical system and, therefore, has a natural frequency. As noted, the value of the natural frequency depends on the configuration and boundary conditions of the system. Once the system configuration and the boundary conditions are specified for the system, the natural frequency of the system is fixed. When a drive train is excited at the natural frequency, the drive train vibrates or oscillates in a noticeable manner.
Modern vehicles are usually equipped with one or more advanced control systems, such as anti-lock braking systems (ABS), traction control systems (TCS), electronic skid prevention systems (ESP), driving stability control systems, and the like. Drive train vibrations can severely degrade the performance of these control systems. In a worst case scenario, drive train vibrations may make the vehicle undriveable on a surface that has a low coefficient of friction.
Accordingly, the invention provides methods and systems designed to detect drive train vibrations of a vehicle. The invention utilizes a period test and a pattern test for detecting the drive train vibrations. A signal is generated based on an evaluation of the rotational behavior of the individual wheels and the torsional vibrations in a circumferential direction of the wheels. The signal includes a vibration signal that is superimposed on a rigid-body motion signal of the wheel. The period of the vibration signal is determined and if the determined period is within the vicinity of the natural frequency of the vehicle drive train, the pattern of the vibration signal is evaluated.
The period test is calibrated using a period calibration parameter or value that is determined by measuring the average value of the vibration signal period during vehicle tests. A vehicle test is typically performed on a representative number of vehicles for each type or model of vehicle. Different types of cars have different system configurations and boundary conditions, and, therefore, have different natural frequencies for their respective vibration signals. The vibration signal period is the inverse of the vibration signal frequency (i.e., the natural frequency of the drive train). Some examples of parameters that affect the natural frequency include: transmission type (automatic or manual transmission), drive train type (front wheel drive, rear wheel drive, or four wheel drive), and the size of components such as the drive shaft and the suspension. The period test is also calibrated to account for variations in the natural frequency of the drive train that may occur over the life of a vehicle as a result of wear and tear of drive train components.
The pattern test is used to ensure that the determined period of the vibration signal is indicative of drive train vibrations and not of some other phenomena such as oscillations caused by vehicle travel over rough surfaces. Without the pattern test, a false positive result or erroneous detection of drive train vibrations could occur.
As is apparent from the above, it is an advantage of the present invention to provide a system and method of detecting vibrations in the drive train of a vehicle. Other features and advantages of the present invention will become apparent by consideration of the detailed description and accompanying drawings.